Interference between Spring Cereals and Kochia scoparia Related to Environment and Photosynthetic Pathways

Abstract

Kochia [Kochia scoparia (L.) Schrad.; syn. Bassia scoparia (L.) A.J. Scott] is a weed that infests cereal crops in the Great Plains of the USA, often severely reducing yields. Herbicides have controlled kochia, but recently kochia has developed resistance to many herbicides. Nonherbicide alternatives are therefore needed for the integrated management of kochia. Greenhouse and growth chamber competition studies were conducted between kochia, a C4 weed, and barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) to determine the environmental conditions that would render kochia most vulnerable to competition by a small‐grain crop. Replacement‐series experiments between kochia and wheat or barley were conducted under various temperature, soil moisture, and light conditions. Unlike wheat, kochia growth and photosynthesis were suppressed under cool temperatures. Barley suppressed kochia more than wheat did because of its larger canopy, despite its lower photosynthetic rates. Under high radiation conditions and warm temperatures, growth and photosynthesis were greater for kochia than wheat. Warm temperatures also increased dark respiration and reduced water use efficiency under low radiation conditions, however, thus limiting kochia's competitiveness under a closed canopy. Water stress did not affect competition, although net photosynthetic rates of kochia were greater at photosynthetically active radiation (PAR) values > 400 μmol m−2 s−1. Growth and CO2 exchange rates varied among four different kochia accessions, but growth of all accessions was reduced by shade. Results suggest that a leafy, cold‐tolerant crop or cultivar, grown early in the season to produce necessary ground cover, should provide opportunity to suppress kochia.

Response of Barley to Grasshopper Defoliation in Interior Alaska: Dry Matter and Grain Yield

“…They reported that weedy vegetation in Þelds that had been cultivated for Ͼ2 yr became dominated by nonnative weed species such as common lambsquarters, common chickweed, Stellaria media (L.) Cyrillo; quackgrass, Agropyron repens (L.) Beauv. ; and foxtail barley, Hordeum jubatum L. In addition, barley is known to be very competitive with weeds, requiring high densities of weeds to reduce yields (Conn and Thomas 1987, Lutman et al 1994, Christensen 1995, Fischer et al 2000, Walker et al 2001. In Alaska, Conn and Thomas (1987) reported a 36% reduction in barley yield in Alaska with 1,300 common lambsquarters seedlings per m 2 , much higher numbers than were encountered in the current study.…”

The biology of Canadian weeds. 138. Kochia scoparia (L.) Schrad.

“…As described previously, earlier spring emergence of the ALS inhibitor-HR cohorts may allow some selective control of HR vs. HS biotypes with spring seedbed preparation (tillage or herbicides) or by early spring frosts. In contrast to delayed seeding to reduce populations (Eberlein and Fore 1984), early seeding of spring crops is suggested to reduce the competitive ability of kochia (Fischer et al 2000). In a growth room study, shoot biomass of wheat was greater than kochia at 158C, but not at 23 or 308C, suggesting that early seeded spring wheat would have a competitive advantage over kochia (Nord et al 1999).…”

Interference interactions of two rice cultivars and their F3cross with barnyardgrass (Echinochloa crus-galli) in a replacement series study

“…Some RYTs were relatively higher than 1.0. This response probably occurred primarily because of the reduced interference in mixtures in relation to the monocultures due to the differences in paths of resource acquisition (Fischer et al 2000) by C 3 rice plants and C 4 BYG plants, respectively.…”